The present invention relates to an artificial satellite tracking system which is mounted on a mobile body movable from one place to another place and controls the attitude of a communication antenna such that the antenna is directed to a communication satellite or the like, and more particularly to an X-Y mount type antenna drive mechanism which drives the antenna.
In an antenna supporting mechanism of an antenna drive system for attitude angle control of antenna which is fixedly mounted on the ground or is mounted on a mobile body such as an automobile, the most popular structure is an Azimuth-Elevation (hereinafter abbreviated xe2x80x9cAZ-ELxe2x80x9d) mount, an X-Z mount or a theodolite which is described on page 194 of xe2x80x9cArtificial satellitexe2x80x9d written by Hiroshi Tsuru (published by Kogaku Tosho Kabushiki Kaisha in 1983). Alternately, the most popular structure may be a structure called an X-Y mount that is described on page 194 or page 195 of the same literature.
In an artificial satellite having a low elevation angle such as a broadcasting satellite on a geostationary orbit, the communication radio waves are often interrupted in an urban district having many tower buildings so that it is difficult to obtain high-quality communication with less interruption of communication radio waves. The high quality communication can be realized by making use of an artificial satellite having a high elevation angle in the zenith direction (a semi-geostationary orbit artificial satellite such as a semi-zenith artificial satellite or an extended elliptical orbit artificial satellite). However, the conventional tracking system for such an artificial satellite having a high elevation angle has the following tasks.
With respect to the AZ-EL mount of the prior art, in tracking of the artificial satellite in the zenith direction, there has been a drawback that an axial speed in the azimuth angle is increased and hence, the possible tracking range is restricted. However, since no consideration has been paid to the expansion of the possible tracking range, there exists a task that the restriction on an artificial satellite that can be tracked must be removed. Further, an AZ axis (an Azimuth axis) is required to have a rotational angle of not less than 360 degrees and hence, a rotary-type wave guide for transmitting transmission/reception signals from an antenna to a mobile body becomes necessary. However, no consideration has been paid to the quality of the signal transmission such that the rotary-type wave guide has a large transmission loss and further no small-sized and light-weighted wave guide that can transmit two ways comprised of transmission and reception has been developed. Accordingly, there exists a task that the transmission loss must be reduced.
On the other hand, with respect to the X-Y mount of the prior art, when the artificial satellite passes in the vicinity of the zenith, a situation that the axial speed in the azimuth angle is extremely increased as in the case of the AZ-EL mount can be obviated. Accordingly, this X-Y mount is applicable to the continuous tracking of an artificial satellite disposed at a position having a large elevation angle.
However, in the oscillating axes arrangement of the X-Y mount of the prior art, since the oscillating rotary center axes of an X axis and a Y axis are not present on a same plane, a drive mechanism such as a drive motor for the Y axis is inevitably mounted above a rotary mechanism relevant to the X axis so that it gives rise to a so-called two-storied constitution. Accordingly, a mechanical portion becomes large-sized and hence, when the mechanical portion is mounted on a mobile body, the maximum vehicle height becomes high and an antenna may largely extend from the vehicle width depending on the axial direction. Accordingly, it is often the case that an antenna portion is accommodated in the mobile body when the mobile body is traveling and the antenna is extended and used when the mobile body is stopped. Further, no consideration has been made with respect to enabling the tracking of an artificial satellite by the mobile body during the traveling and hence, there exists a task that the mechanism must be small-sized and light-weighted. To consider the fact that the mechanism is mounted on the mobile body, two points are important. That is, the height of the device is important from the viewpoint of the wind pressure and the traveling stability and the weight of the device is important in view of the withstanding load of a ceiling of the mobile body.
Provided that the antenna per se is not changed, by reviewing the constitution and the arrangement of drive systems such as drive motors for operating the antenna and the weight balancing of members provided for mounting them, it becomes possible to make the device small-sized and light-weighted.
It is an object of the present invention to make a mechanical system small-sized and light-weighted by optimizing the constitution, the arrangement and the weight balancing of a drive system of an antenna mechanism for supporting transmission/reception antennas whereby a high quality communication can be realized by tracking a semi-geostationary orbit artificial satellite such as an extended elliptical orbit artificial satellite or a semi-zenith artificial satellite from a traveling mobile body.
To achieve the above-mentioned object, in an X-Y mount type antenna drive device comprising an antenna portion which includes an antenna capable of performing at least either one of transmission or reception, a fixed supporting portion which supports the antenna portion, and a oscillating mechanism which is disposed between the antenna portion and the fixed supporting portion and has rotational degrees of freedom on an X-Y plane parallel to a plane of the antenna, the antenna drive device further comprises an antenna supporting portion which supports the antenna portion, a first oscillating mechanism portion which oscillates the antenna portion and the antenna supporting portion about a first oscillating axis, and a second oscillating mechanism portion which oscillates the first oscillating mechanism portion relative to the fixed supporting portion about a second oscillating axis, and the center of gravity of the first oscillating mechanism portion is disposed in the vicinity of an oscillating center line of the second oscillating axis. Due to such a constitution, the center of gravity of the first oscillating mechanism approaches the oscillating center axis of the second oscillating mechanism so that the moment of inertia can be reduced whereby it becomes possible to reduce the required torque of drive motors and the size of motors and to make the mechanism portion small-sized and light-weighted. Accordingly, it is preferable to arrange a heavy X-axis motor above the oscillating center axis of the Y-axis.
Further, to achieve the above-mentioned object, the oscillating center axis can be in the same member. Due to such a constitution, if the antenna is supported by two parts such as antenna supporting longitudinal plates connecting an antenna to a first oscillating mechanism portion, the deviation of axis between the antenna supporting longitudinal plates can be eliminated and hence, the shaft strength is increased. Further, since the axial alignment becomes unnecessary, the assembling of the device starting from a base portion becomes facilitated thus enhancing the reliability and maintenance of the device.
Additionally, to achieve the above-mentioned object, adapters disposed between the antenna supporting longitudinal plates of antenna supporting portion and the oscillating center axis may be preferably replaceable. By using the adapters disposed in the midst of the antenna supporting longitudinal plates replaceable, the adjustment of the operating range becomes possible without changing the drive mechanism of X-Y axes or the antenna supporting portion so that the standardization becomes possible and the cost can be reduced.
Further, to achieve the above-mentioned object, the antenna holding plate portion of the antenna supporting portion for holding the transmission and reception antennas may have a circular disc shape in place of a rectangular parallelepiped shape. This can be achieved by cutting and rounding four corners of the rectangular parallelepiped of the holding plate portion. The position of the oscillating center axis in the operation state just before a holding plate portion holding the antenna as a part of the antenna supporting portion interferes with a constituent member such as an antenna base (e.g. a pedestal) becomes the height of the oscillating center axis and is used as a base for calculating the device height of the whole antenna mechanism. When the both X-Y axes approach the operational limit, the holding plate portion interferes with the antenna base or the like and this interference depends on the length of a diagonal line of the antenna holding plate. Accordingly, by providing the shape of the holding plate portion as a circular shape, the length of the diagonal line can be shortened and hence, the device height of the whole antenna mechanism can be decreased.
Further, to achieve the above-mentioned object, a control of the antenna may preferably be performed such that the first and second oscillating axes are driven by converting command values in a form of an azimuth angle and an elevation angle into oscillating angles of the first and second oscillating axes so as to control the azimuth angle and the elevation angle of the antenna. By operating the antenna in response to the command values of the azimuth angle and the elevation angle, the artificial satellite tracking system can be used as a mount mechanism of an X-Z form, whereby the applicability of the system can be enlarged.
Additionally, to achieve the above-mentioned object, in an artificial satellite tracking system according to the present invention comprising antennas that transmit and receive radio waves with respect to an artificial satellite, an antenna drive mechanism that drives the antennas with rotational degrees of freedom on an X-Y plane parallel to an antenna plane, a control part that performs a drive control of the antenna drive mechanism in response to signals received by the antennas, and a communication equipment that performs communication with the artificial satellite through the antennas, the antenna drive mechanism includes an antenna holding portion holding the antennas, supporting legs supporting the antenna holding portion, an X-axis base portion tiltably holding the antennas by way of the supporting legs, an X-axis drive motor mounted in a space defined by the supporting legs on the X-axis base portion and drives the supporting legs, and a fixed supporting portion having a oscillating mechanism that oscillates the X-axis base portion relative to a Y-axis that passes through the X-axis drive motor or is disposed above the X-axis drive motor.